(a) Field of the Invention
The present invention relates to a polishing composition for planarizing a metal layer. Its object is to provide a polishing composition for use in chemical mechanical polishing, thus capable of improving the planarization effect of a work piece.
(b) Description of the Prior Art
With the critical dimension of an electronic component becoming more and more compact and the wiring layer number thereof rapidly increasing, the RC time delay significantly affects the operation speed of the entire circuits. In order to improve the problems of the time delay and the reliability of electron migration due to the reduction in metal line width, copper conductor material with low resistivity and high resistance to damage by electron migration is selected to replace aluminum alloys. However, it needs to employ another damascene process in forming copper conductors because copper metal is difficult to be etched.
Damascene processes are different from traditional metallization processes, in which metallic patterns are initially defined, followed by filling trenches with dielectric layers. In the damascene process, a conductive line trench is first etched in a flat dielectric layer, filling a metal layer therein, and finally removing excess metal to obtain a flat structure with metal inlayed in the dielectric layer. Damascene processes have the following advantages in comparison with traditional metallization processes: (1) the surface of a substrate is always kept flat; (2) the drawback that dielectric material is difficult to be filled into the spacing between metallic conductors in traditional processes can be eliminated; (3) the difficulty in etching metallic material, especially in etching copper metal could be solved.
Moreover, in order to overcome the drawback that the necessity of separately fabricating a contact window structure and a conductor pattern makes the fabrication procedures of a traditional interconnection process extremely complicated, currently, a dual damascene process is further developed. In the dual damascene process, a line dielectric and a via dielectric are respectively etched off by two times of selective etching, completing the barrier layers of the metal layer and of the plug at a time, then filling conductive metal into the vias and interconnection trenches at a time, so as to simplify the fabrication procedures. In recent years, copper metal with low resistivity and high resistance to electron migration has been gradually used as the material of metal interconnects instead of aluminum metal in the prior process technology to meet the requirement for miniaturizing the components and increasing the operation speed thereof. Copper damascene interconnection technology not only can achieve the miniaturization of interconnects and the reduction of RC time delay, but also can solve the difficulty in etching metallic copper. Therefore, it has become the main trend of the development of multiple interconnections today.
Regardless of in a single damascene or in a dual damascene copper process, after the completion of the copper metal filling, it needs to perform a planarization process for removing excess metal on the dielectric layer. Currently, this purpose is usually achieved by a chemical mechanical polishing process. However, in metal chemical mechanical polishing, polishing defects such as dishing, erosion and the like still often occur on the surface of a metal layer.
Dishing and erosion are strongly associated with the removal rate and RR/DER ratio. A lower removal rate can ensure a low removal rate on a pattern recess to effectively suppress dishing defects, but in view of the throughput of the unit, the removal rate must be maintained within an acceptable range. Furthermore, the polishing uniformity affects the planarity to a certain extent. More polishing time is required for completely removing copper with poorer uniformity, thus causing more serious dishing and erosion problems.
To give consideration to both the throughput of the unit and the suppression of dishing and erosion, a copper chemical mechanical polishing process is often divided into two stages. In the first stage, most copper is removed at a higher removal rate to increase the throughput of the unit. In the second stage, a small amount of the remaining copper is polished off at a lower removal rate to prevent the copper in the trenches from excessive erosion. In general, a two-stage copper polishing process needs to change polishing compositions of different formulations to satisfy the requirements in the various stages for polishing copper. However, the changing of polishing compositions is disadvantageous to process simplification as well as increases the waste.
A polishing composition disclosed in US patent 2008/0254629 comprises an amino acid, about 5 ppm to less than 700 ppm abrasive particulate material by weight, a triazole compound and water, wherein the ratio of copper rate of removal relative to the stop layer rate of removal, i.e., the selectivity, is greater than 50:1. US Patent Publication No. 2004/0020135 disclosed a copper polishing composition comprising silica, an oxidant, an amino acid, a triazole compound and water. Furthermore, U.S. Pat. No. 6,440,186 disclosed a polishing composition containing: an abrasive, a protective film forming agent and hydrogen peroxide, wherein the abrasive has a particle size from 50 to 120 nm and is in an amount of from 0.5 to 5 wt % (percent by weight) based on the total weight of the composition. Moreover, U.S. Pat. No. 6,679,929 disclosed a polishing composition comprising an abrasive, an aliphatic carboxylic acid having at least 10 carbon atoms, a basic compound selected from ammonium hydroxide etc., a polishing accelerating compound, an anticorrosive, hydrogen peroxide and water. However, the above patents do not disclose that a polishing composition employing a dual-inhibitor could decelerate the metal etching rate under the condition of maintaining a high removal rate and meanwhile was suited to the first and second stages for polishing copper metal.